Free-space optical (FSO) systems include network nodes that communicate with one another optically using beams of light. FSO systems can provide much higher data rates than radio frequency (RF) communication systems. FSO systems are also often free from spectrum usage restrictions associated with RF systems. In addition, FSO systems typically offer a lower probability of detection and higher jam resistance than RF systems. However, when used in the atmosphere, FSO systems are susceptible to blockage by clouds, fog, and other obstructions, and FSO systems can suffer from deep fades even in clear atmosphere due to turbulence.
Conventional solutions to these problems include mitigation techniques at the optical link level, hybrid RF/optical links, and network-based protection approaches. Link mitigation techniques typically involve features such as adaptive optics, forward error correction, interleaving, and optical automatic gain control. However, even with these mitigation techniques, FSO systems often have difficulty providing acceptable performance even in clear air. Hybrid RF/optical links fall back on RF communications when optical communications fail, but RF links have significantly less range and throughput than optical links, thereby reducing system throughput. Link-based mitigation has been augmented with network-based approaches, which typically rely on large buffers, retransmissions once optical links are restored, and the establishment of new optical links using mechanical beam steering. Unfortunately, these techniques typically introduce large latencies and have limited scalability to large networks. In addition, cost along with size, weight, and power (SWaP) considerations restrict the number of optical terminals (and therefore the number of optical links) that can be used at a network node, particularly for moving platforms such as aircraft and ground vehicles. This typically makes maintaining backup paths impractical when using mechanical beam steering.